ORIGINAL: BMatthews
ORIGINAL: h-ray-RCA
....
Upper wing: 5 3/8” chord
Lower wing: 4 ¼” chord
Overlap: 1 ½”
Effective span: 6 7/8”
25% of 6 7/8= 1.71” should be the actual CG.
Mfg lists cg as being 3 ½” from LE of upper wing.
The overlap should be listed as the lower exposure I think. Otherwise the numbers don't add up.
The picture tells a 1000 words and those words are saying "THEY ARE NUTS! ! !". You're right to question that location. I don't know where they got that number but it would be a disaster looking for a place close by to happen at takeoff time. I'd go with 1.7 to 1.75 from the upper leading edge and see how it works out for the test flight. That would be a safe starting point for sure.
when in doubt -make a paper drawing of the plane -in planform this will show the both wings as just part of a fat chord
use that "fat chord" as basis for the cg location